This invention provides a regioselective synthesis of CCl-779, which is useful as an antineoplastic agent.
Rapamycin 42-ester with 3-hydroxy-2-(hydroxymethyl)-2-methylpropionic acid (CCl-779) is an ester of rapamycin which has demonstrated significant inhibitory effects on tumor growth in both in vitro and in vivo models.
CCl-779 may delay the time to progression of tumors or time to tumor recurrence which is more typical of cytostatic rather than cytotoxic agents. CCl-779 is considered to have a mechanism of action that is similar to that of sirolimus. CCl-779 binds to and forms a complex with the cytoplasmic protein FKBP, which inhibits an enzyme, mTOR (mammalian target of rapamycin, also known as FKBP12-rapamycin associated protein [FRAP]). Inhibition of mTOR's kinase activity inhibits a variety of signal transduction pathways, including cytokine-stimulated cell proliferation, translation of mRNAs for several key proteins that regulate the G1 phase of the cell cycle, and IL-2-induced transcription, leading to inhibition of progression of the cell cycle from G1 to S. The mechanism of action of CCl-779 that results in the G1-S phase block is novel for an anticancer drug.
In vitro, CCl-779 has been shown to inhibit the growth of a number of histologically diverse tumor cells. Central nervous system (CNS) cancer, leukemia (T-cell), breast cancer, prostate cancer, and melanoma lines were among the most sensitive to CCl-779. The compound arrested cells in the G1 phase of the cell cycle.
In vivo studies in nude mice have demonstrated that CCl-779 has activity against human tumor xenografts of diverse histological types. Gliomas were particularly sensitive to CCl-779 and the compound was active in an orthotopic glioma model in nude mice. Growth factor (platelet-derived)-induced stimulation of a human glioblastoma cell line in vitro was markedly suppressed by CCl-779. The growth of several human pancreatic tumors in nude mice as well as one of two breast cancer lines studied in vivo also was inhibited by CCl-779.
The preparation and use of hydroxyesters of rapamycin, including CCl-779, are disclosed in U.S. Pat. No. 5,362,718. A regiospecific synthesis of CCl-779 is described in U.S. Pat. No. 6,277,983.
CCl-779 can be synthesized by the non-regioselective acylation of rapamycin, as described in U.S. Pat. No. 5,362,718. The synthesis, however, is complicated by mixtures of the desired 42-ester, with 31-esterified rapamycin, as well as 31, 42-diesterified rapamycin and unreacted rapamycin.
CCl-779 can also be prepared by the acylation of the 31-silyl ether of rapamycin with a ketal of bis-(hydroxymethyl)propionic acid, followed by removal of the 31-silyl ether and ketal protecting group from the bis-(hydroxymethyl) propionic acid, as described in U.S. Pat. No. 6,277,983. However, the crude 42-monoester produced from this regioselective synthesis requires further purification by column chromatography to remove residual amounts of diester by-products and unreacted rapamycin starting material.